System and method for detecting aerial vehicle position and velocity via sound

ABSTRACT

A system for determining a signal source position and velocity, and methods for manufacturing and using same are provided. An exemplary method includes determining a signal source position and velocity by performing a direction analysis on a plurality of audio signals and performing an intensity analysis on the audio signals. Another exemplary method includes determining that a signal source is on a collision course with a moving platform and providing an instruction for altering the course of the moving platform to avoid a collision with the signal source. An exemplary system includes an acoustic sensing system, having a primary microphone array, a secondary microphone, and a processing device for determining a signal source position and velocity by performing a direction analysis on a plurality of audio signals and performing an intensity analysis on the audio signals.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application of International Application No.PCT/CN2015/072160, filed on Feb. 3, 2015, the entire contents of whichare incorporated herein by reference.

FIELD

The present disclosure relates generally to object detection and moreparticularly, but not exclusively, to determining a signal sourceposition and velocity.

BACKGROUND

With the development of unmanned aerial vehicles, aerial safety issueshave received more attention. In a sky domain, there are often manyaircraft, including airplanes and unmanned aerial vehicles. In manysituations, these aircraft cannot communicate with each other directly,and, thus, it is difficult for a selected aircraft to know the velocityand position of other aircraft in the area. Conventional solutionsinclude use territorial radar to detect the position and velocity ofaircraft or relying on the vision of aircraft operators to avoid otheraircraft. However, these approaches are not easily applicable to smallunmanned aerial vehicles that are not easily observable by radar andthat cannot rely on the vision of human operators. Unfortunately,current solutions fail to adequately provide for aerial vehicles capableof self-determination and self-detection (i.e., autonomous determinationand detection of other aircraft).

In view of the foregoing, a need exists for an improved aerial vehicleposition and velocity detection system in an effort to overcome theaforementioned obstacles and deficiencies of conventional systems.

SUMMARY

One aspect includes a method of determining a signal source position andvelocity that includes performing a direction analysis on a plurality ofaudio signals and performing an intensity analysis on the audio signals.In one embodiment, at least one of the performing the direction analysisand the performing the intensity analysis is based on a Doppleranalysis. Another embodiment also includes obtaining a first set ofaudio signals from a primary microphone array. Another embodiment alsoincludes obtaining a first noise audio signal from a secondarymicrophone. A further embodiment includes subtracting the noise audiosignal from each audio signal in the first set. A still furtherembodiment includes generating a first set of processed audio signalsbased on the subtracting.

One embodiment includes conducting a frequency estimation on the firstset of processed audio signals. Another embodiment includes determininga signal direction of a first signal source based on the first set ofprocessed audio signals. A further embodiment includes generating asecond set of processed audio signals based on the subtracting. A stillfurther embodiment includes conducting a frequency estimation on thesecond set of processed audio signals. Yet another embodiment includesdetermining a signal direction of a first signal source based on thesecond set of processed audio signals.

One embodiment includes determining whether the signal source isapproaching or moving away from a detection position. Another embodimentincludes determining whether the signal source is approaching or movingaway from a detection position comprises performing a Doppler analysisof the first and second set of processed audio signals. A furtherembodiment includes determining a signal source distance from thedetection position. In a still further embodiment, determining a signalsource distance from the detection position comprises a determinationbased on a received signal intensity. Yet another embodiment includespredicting a future signal source position and velocity based on theperforming the Doppler analysis, based on the performing the directionanalysis and based on the performing the intensity analysis of aplurality of audio signals.

Another aspect includes a method of dodging a signal source thatincludes determining that a signal source is on a collision course witha detection position of a moving platform based on a determined signalsource position and velocity determined by an embodiment of the methoddescribed above and dodging the signal source by altering the course ofthe moving platform.

In one embodiment, the altering the course of the moving platformcomprises moving in an opposite direction of from the determined signalsource position. In another embodiment, the altering the course of themoving platform comprises moving in an orthogonal direction from thedetermined signal source position. In a further embodiment, the alteringthe course of the moving platform comprises moving around the determinedsignal source position. In a still further embodiment, the altering thecourse of the moving platform comprises ceasing movement and hovering inplace. In one embodiment, the moving platform is an aerial vehicle. Inanother embodiment, the aerial vehicle is an unmanned aerial vehicle.

A further aspect includes a computer program product for determining asignal source position and velocity, the computer program product beingencoded on one or more machine-readable storage media and comprisinginstruction for executing the embodiments described above. A stillfurther aspect includes a computer program product for dodging a signalsource, the computer program product being encoded on one or moremachine-readable storage media and comprising instruction for executingthe embodiments described above.

One aspect includes a computer program product, wherein the embodimentsof determining a signal source position and velocity as described aboveare provided as a series of instructions stored on non-transitorystorage medium. Another aspect includes a computer program product,wherein the embodiments of dodging a signal source as described aboveare provided as a series of instructions stored on non-transitorystorage medium.

A further aspect includes a computer program product for determiningoptical-flow in physical space, the computer program product beingencoded on non-transitory machine-readable storage media and includinginstruction for subtracting a noise audio signal from each of aplurality of audio signals of a first set of audio signals to generate afirst set of processed audio signals, instruction for conducting afrequency estimation on the first set of processed audio signals,instruction for determining a signal direction of a first signal sourcebased on the first set of processed audio signals, instruction forgenerating a second set of processed audio signals, instruction forconducting a frequency estimation on the second set of processed audiosignals, instruction for determining a signal direction of a firstsignal source based on the second set of processed audio signals,instruction for determining a signal direction of a first signal sourcebased on the second set of processed audio signals, instruction fordetermining whether the signal source is approaching or moving away froma detection position, instruction for determining whether the signalsource is approaching or moving away from a detection position comprisesperforming a Doppler analysis of the first and second set of processedaudio signals, and instruction for determining a signal source positionand velocity based on the Doppler analysis, the direction analysis andthe distance analysis.

A further aspect includes a computer program product for determiningoptical-flow in physical space, the computer program product beingencoded on non-transitory machine-readable storage media and includinginstruction for conducting a frequency estimation on a first set ofaudio signals, instruction for determining a signal direction of a firstsignal source based on the first set of audio signals, instruction forconducting a frequency estimation on a second set of audio signals,instruction for determining a signal direction of a first signal sourcebased on the second set of audio signals, instruction for determining asignal direction of a first signal source based on the second set ofaudio signals, instruction for determining whether the signal source isapproaching or moving away from a detection position, instruction fordetermining whether the signal source is approaching or moving away froma detection position comprises performing a Doppler analysis of thefirst and second set of audio signals; and instruction for determining asignal source position and velocity based on the Doppler analysis, thedirection analysis and the distance analysis.

One aspect includes a method of determining a signal source position andvelocity that includes conducting a frequency estimation on a first setof audio signals, determining a first signal direction of a signalsource based on the first set of audio signals, conducting a frequencyestimation on a second set of audio signals, determining a second signaldirection of the signal source based on the second set of audio signals,determining whether the signal source is approaching or moving away froma detection position by performing a Doppler analysis of the first andsecond set of audio signals, determining a signal source distance fromthe detection position based on signal intensity of the first and secondset of audio signals, and determining a signal source position andvelocity based on the Doppler analysis, the direction analysis and theintensity analysis. One embodiment also includes predicting a futuresignal source position and velocity based on the Doppler analysis, thedirection analysis and the intensity analysis.

Another aspect includes a method of dodging a signal source thatincludes determining that a signal source is on a collision course witha detection position on a moving platform based on a determined signalsource position and velocity determined by the method of determining asignal source position and velocity according to the aspect above; anddodging the signal source by altering the course of the moving platform.In one embodiment, the moving platform is an aerial vehicle. In anotherembodiment, the aerial vehicle is an unmanned aerial vehicle.

A further aspect includes a system for determining a signal sourceposition and velocity, wherein the system implements an embodimentdescribed above. Yet another aspect includes a system for dodging asignal source, wherein the system implements embodiment described above.

One aspect includes a computer program product for determining a signalsource position and velocity, the computer program product being encodedon one or more machine-readable storage media and comprising instructionfor executing an embodiment described above. Another aspect includes acomputer program product for dodging a signal source, the computerprogram product being encoded on one or more machine-readable storagemedia and comprising instruction for executing an embodiment describedabove.

A further aspect includes a computer program product, wherein the methodof determining a signal source position and velocity as described in anembodiment above is provided as a series of instructions stored onnon-transitory storage medium. A still further embodiment includes acomputer program product, wherein the method of dodging a signal sourceof an embodiment described above is provided as a series of instructionsstored on non-transitory storage medium.

One aspect includes an acoustic sensing system that includes a firstprimary microphone array; a secondary microphone; and a processingapparatus for determining a signal source position and velocity based ona Doppler analysis, a direction analysis and an intensity analysis of aplurality of audio signals.

Another aspect includes an acoustic sensing system that includes ahousing, a first primary microphone array positioned on the housing andcomprising a plurality of microphones, a first secondary microphonepositioned on the housing, the first secondary microphone operablyconnected to the first primary microphone array, and a processing devicefor determining a signal source position and velocity based on adirection analysis and an intensity analysis of a plurality of audiosignals.

In one embodiment, the determining a signal source position and velocityis further based on a Doppler analysis. In another embodiment, the firstprimary microphone array and first secondary microphone are positionedin parallel, but different, planes on the housing. In a furtherembodiment, the first primary microphone array points in a firstdirection and the first secondary microphone points in a seconddirection that is different than the first direction. In a still furtherembodiment, the first direction is opposite of the second direction. Inyet another embodiment, the first direction is substantiallyperpendicular of the second direction.

In one embodiment, the microphones of the first primary microphone arrayare positioned on a substrate in a matrix configuration having rows andcolumns. In another embodiment, the microphones of the first primarymicrophone array are positioned in substantially the same plane.

One embodiment includes a processor and a memory positioned within thehousing and operably connected to the first primary microphone array andthe first secondary microphone. Another embodiment includes a secondprimary microphone array positioned on the housing and operablyconnected to the first primary microphone array and the first secondarymicrophone. A further embodiment includes a second secondary microphonepositioned on the housing and operably connected to the first and secondprimary microphone array and the first secondary microphone.

In one embodiment, the first primary microphone array points in a firstdirection, the first secondary microphone points in a second direction,the second primary microphone array points in a third direction, thesecond secondary microphone points in a fourth direction; and at leasttwo of the first, second, third and fourth directions are differentdirections. In another embodiment, the first direction is opposite ofthe second direction and the third direction is opposite of the fourthdirection

In one embodiment, the first primary microphone array and firstsecondary microphone are positioned in parallel, but different, planeson the housing; and the second primary microphone array and secondsecondary microphone are positioned in parallel, but different, planeson the housing that are substantially perpendicular to the first primarymicrophone array and first secondary microphone position. In anotherembodiment, the first primary microphone array and first secondarymicrophone are configured to detect ultrasonic sound. In a furtherembodiment, the first primary microphone array and first secondarymicrophone are configured to detect subsonic sound.

In one embodiment, the processing device is further configured tosubtract a background noise audio signal obtained by the secondarymicrophone from each of a plurality of audio signals of the first set ofaudio signals to generate a first set of processed audio signals. Inanother embodiment, the processing device is further configured toconduct a frequency estimation on the first set of processed audiosignals. In a further embodiment, the processing device is furtherconfigured to determine a signal direction of a signal source based onthe first set of processed audio signals. In yet another embodiment, theprocessing device is further configured to generate a second set ofprocessed audio signals.

In one embodiment, the processing device is further configured toconduct a frequency estimation on the second set of processed audiosignals. In another embodiment, the processing device is furtherconfigured to determine a second signal direction of the signal sourcebased on the second set of processed audio signals. In a furtherembodiment, the processing device is further configured to determinewhether the signal source is approaching or moving away from a detectionposition. In a still further embodiment, the processing device isfurther configured to determine a signal source distance from thedetection position. In yet another embodiment, the processing device isfurther configured to predicting a future signal source position andvelocity based on the Doppler analysis, the direction analysis and theintensity analysis of a plurality of audio signals.

Another aspect includes a moving platform that includes a housing, afirst primary microphone array positioned on the housing and comprisinga plurality of microphones, a first secondary microphone positioned onthe housing, the first secondary microphone operably connected to thefirst primary microphone array, and a processing device for determininga signal source position and velocity based on a direction analysis andan intensity analysis of a plurality of audio signals the acousticsensing system. In one embodiment, the moving platform is an unmannedaerial vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary network drawing illustrating an embodiment of asystem for determining a signal source position and velocity.

FIG. 2 is an exemplary network drawing illustrating an alternativeembodiment of the system, wherein the system further comprises asecondary microphone.

FIG. 3 is an exemplary side-view drawing illustrating an embodiment ofthe system for determining a signal source position and velocity of FIG.2, wherein the system is positioned on a housing.

FIG. 4 is an exemplary network drawing illustrating an alternativeembodiment of the system for determining a signal source position andvelocity of FIG. 2, wherein the system is operably connected to a mobileplatform.

FIG. 5 is an exemplary detail drawing illustrating a higher signalfrequency generated by the Doppler effect when a second mobile platformis moving toward the mobile platform of FIG. 4.

FIG. 6 is an exemplary detail drawing illustrating a lower signalfrequency generated by the Doppler effect when a second mobile platformof FIG. 4 is moving toward the mobile platform of FIG. 4.

FIG. 7 is an exemplary flow diagram illustrating an embodiment of amethod of aerial vehicle detection and avoidance.

FIG. 8 is an exemplary flow diagram illustrating another embodiment of amethod of aerial vehicle detection and avoidance.

FIG. 9 is an exemplary flow diagram illustrating a method of identifyingthe position and velocity of a signal source such as an aerial vehicle.

FIG. 10 is an exemplary flow diagram illustrating another method ofidentifying the position and velocity of a signal source such as anaerial vehicle.

FIG. 11 is an exemplary flow diagram illustrating a further method ofidentifying the position and velocity of a signal source such as anaerial vehicle.

FIG. 12 is a set of three graphs that illustrate examples of aerialvehicle audio signatures.

FIG. 13 is a set of three graphs that illustrate examples of audiosignals received by the system of FIG. 1 or 2, wherein the systemdetermines that the signals correspond to the respective aerial vehicleaudio signatures of FIG. 12.

FIG. 14 is an exemplary graph illustrating the relationship between achange of the reciprocal of the inner product based on frequency duringimplementation of the MUSIC algorithm.

FIG. 15 is an exemplary graph illustrating that the signal space canchange with a change of the incidence angle of a signal duringimplementation of the MUSIC algorithm.

FIG. 16 an exemplary network diagram that illustrates a first aerialvehicle that is operably connected to a base station via a network.

FIG. 17 is a detail drawing illustrating an alternative embodiment ofthe detection system of FIG. 2, wherein the system is positioned on afirst aerial vehicle and includes first and second microphone arrays andfirst and second secondary microphones positioned on opposing sides ofthe aerial vehicle and pointing in opposite directions.

FIG. 18 is a detail drawing illustrating an alternative embodiment ofthe detection system of FIG. 17, the first and second microphone arraysand the first and second secondary microphones are positionedperpendicularly on the aerial vehicle and pointing outwardly.

FIG. 19 is a detail drawing illustrating another alternative embodimentof the detection system of FIG. 1, where the detection system includes asingle microphone array.

FIG. 20 is a detail drawing illustrating still further alternativeembodiment of a detection system of FIG. 19, where the detection systemincludes four separate microphone arrays positioned on an aerialvehicle.

It should be noted that the figures are not drawn to scale and thatelements of similar structures or functions are generally represented bylike reference numerals for illustrative purposes throughout thefigures. It also should be noted that the figures are only intended tofacilitate the description of the exemplary embodiments. The figures donot illustrate every aspect of the described embodiments and do notlimit the scope of the present disclosure.

DETAILED DESCRIPTION

Since currently-available aerial vehicle position and velocity detectionsystems are deficient, a system for determining a signal source positionand velocity using sound can prove desirable and provide a basis for awide range of applications, such as detection and avoidance ofapproaching aerial vehicles. This result can be achieved, according toone embodiment disclosed herein, by a signal source position andvelocity detection system 100 as illustrated in FIG. 1.

Turning to FIG. 1, the aerial vehicle position and velocity detectionsystem 100 is shown as comprising a primary microphone array 110 beingoperably connected to a sensing device 120 in accordance with oneembodiment. As illustrated in FIG. 1, the sensing device 120 can includea processor 121 and/or a memory 122, which can be separate from (asshown in FIG. 1), or at least partially integrated with, the processor121. In various embodiments, the primary microphone array 110 caninclude a plurality of microphones 112 configured to receive audiosignals and positioned on a substrate 111 in a matrix configuration 114defined by a plurality of rows R and columns C. Although shown ascomprising twenty microphones 112 in the matrix configuration 114 forpurposes of illustration only, the array 110 can include any suitablenumber of microphones 112 positioned in any suitable arrangement. Forexample, as depicted in FIG. 1, the microphones 112 in the array 110 canbe positioned in substantially the same plane and/or evenly spaced in amatrix configuration 114.

Turning to FIG. 2, the aerial vehicle position and velocity detectionsystem 100 is shown as comprising the primary microphone array 110 and asecondary microphone 130 each being operably connected to the sensingdevice 120 in accordance with another embodiment. The secondarymicrophone 130 can include a microphone 112 positioned on a substrate131. As discussed herein, the secondary microphone 130 can be configuredto receive audio noise signals, such as environmental sounds.

Although shown as comprising a single microphone 112 for purposes ofillustration only, the secondary microphone 130 can include any suitablenumber of microphones 112 positioned in any suitable arrangement. Themicrophones 112 of the array 110 and the microphones 112 of thesecondary microphone 130 can be the same and/or different type ofmicrophone. Additionally, each microphone 112 can be operable to detectsound waves of any suitable frequency, including subsonic, sonic, and/orultrasonic frequencies. Suitable types of microphones 112 can include acondenser microphone, a dynamic microphone, a ribbon microphone, acarbon microphone, a piezoelectric microphone, a fiber-optic microphone,a laser microphone, a liquid microphone, a MEMS microphone, or the like,without limitation. Each microphone 112 can have any suitable sensingpattern, including omnidirectional, bi-directional, sub-cardioid,cardioid, hyper cardioid, super cardioid, shotgun, or the like.

Although shown in FIG. 2 as including one primary microphone array 110and one secondary microphone 130 for purposes of illustration only, theposition and velocity detection system 100 can include any suitablenumber of primary microphone arrays 110 and/or secondary microphones 130(see, for example, FIGS. 17 and 18). The primary microphone array 110,in other words, can include one or more microphone arrays, and eachmicrophone array of the primary microphone array 110 can be separateand/or at least partially integrated with another microphone array.Additionally and/or alternatively, the primary microphone array 110 orsecondary microphone 130 can be absent. For example, in someembodiments, noise reduction using the secondary microphone 130 may notbe performed, and therefore the secondary microphone 130 can be absent(see, for example, FIGS. 1, 19 and 20).

As illustrated in FIG. 3, the position and velocity detection system 100can be positioned on a housing 240. For example, the primary microphonearray 110 can be positioned on a first side 241 of the housing 240pointing in a first direction 211A, and the secondary microphone 130 canbe positioned on a second side 242 of the housing 240 pointing in asecond direction 211B. The second direction 211B is opposite to thefirst direction 211A, in other words, the first direction 211A issubstantially perpendicular to the second direction 211B.

Although FIG. 3 illustrates the primary microphone array 110 andsecondary microphone 130 positioned in parallel planes on opposing sidesof the housing 240 and pointing in opposite directions 211A, 111B, forpurposes of illustration only, the primary array 110 and secondarymicrophone 130 can be positioned in any suitable relationship, includingin perpendicular planes, or the like. In other words, an angle (notshown) formed between the first and second directions 111A, 111B cancomprise any suitable angle including 180°, 90°, 45°, or the like,and/or any suitable range of angles. Additionally, some embodiments caninclude any suitable plurality of the array 110 and/or secondarymicrophone 130 in any suitable relationship.

The examples discussed herein relate to detection of position andvelocity of a signal source, such as an Unmanned Aerial Vehicle (UAV) orother aerial vehicle, via sound using the system 100; however, furtherembodiments can relate to detection of position and velocity of otherstationary and/or mobile objects including vehicles, people, animals,devices, or the like, and the disclosed examples and illustrativeembodiments should not be construed to be limiting on the scope of thedisclosed system 100.

Additionally, in some embodiments where the system 100 is positioned onan aerial vehicle, the system 100 can detect the sound signature of theaerial vehicle reflected off of an object and use this detection toavoid the object. For example, the system 100 may use echo-locationtechniques to avoid objects based on an echo of the sound from theaerial vehicle upon which the system 100 is positioned.

Various embodiments can include a ground-based assembly 1105 (shown inFIG. 16) that is configured to detect the position and velocity of atleast one second aerial vehicle 305 (shown in FIG. 16). In otherembodiments, and as depicted in FIGS. 4-6, the system 100 can beoperably connected to and/or positioned on the first aerial vehicle 200,including an Unmanned Aerial Vehicle (UAV). For example, as depicted inFIGS. 5 and 6, the array 110 can be positioned on a first side 315 ofthe first aerial vehicle 200 and the secondary microphone 130 can bepositioned on a second side 320 of the first aerial vehicle 200.

As illustrated in FIG. 4, the first aerial vehicle 200 can include ahousing 201 and a plurality of rotors 202 that are rotatably coupled tothe housing 201. The rotors 202 spin to provide propulsion and rotationcapabilities to the first aerial vehicle 200. The first aerial vehicle200 can emit sound caused by rotation of the rotors 202 and/or a motor(not shown) that powers the rotors 202. This sound can be substantiallyconstant while the first aerial vehicle 200 is operating and can beunique compared to environmental sounds. Being unique for differenttypes of first and/or second aerial vehicles 200, 305 the sound emittedby the first and/or second aerial vehicles 200, 305 can provide a uniqueaudio signature for the first aerial vehicle 200. Accordingly, thisunique audio signature of the operating first and/or second aerialvehicles 200, 305 can be used to determine its position and velocityrelative to the detection system 100 as discussed herein. Additionally,where the detection system 100 is part of the first aerial vehicle 200,detecting the position and velocity of other aerial vehicles 305 canprovide for avoidance of these other aerial vehicles 305 as discussedherein.

Although the first aerial vehicle 200 is shown as being a quad-rotor UAVherein for purposes of illustration only, it should be clear that anysuitable type of first aerial vehicle 200 can include the detectionsystem 100. Additionally, while a first aerial vehicle 200 and/or mobileplatform can include a UAV, the aerial vehicle and/or mobile platformcan additionally and/or alternatively include an airplane, jet,helicopter, or the like.

FIGS. 7 and 8 are flow diagrams illustrating methods 400, 500 of aerialvehicle detection and avoidance in accordance with an embodiment.Referring to FIGS. 7 and 8, in block 420, at least one audio signalcorresponding to at least one aerial vehicle is identified. Identifyingone or more signal corresponding to one or more aerial vehicle can bedone in any suitable manner. For example, as discussed above, the aerialvehicle can emit an audio signature that can be identified as beingdistinct from other ambient sounds. The audio signature can comprise arange of frequencies, a set of frequency peaks, a single frequency peak,and/or a pattern of one or more frequency peak or frequency range.

For example, FIG. 12 includes three graphs 900A, 900B, 900C of exampleaudio signatures 901, 902, 903. The first graph 900A shows an audiosignature 901 that consists of a single frequency peak. The second graph900B shows an audio signature 902 that consists of a grouped range offrequency peaks. The third graph 900C shows an audio signature 903 thatconsists of three separate frequency peaks. In some embodiments,identifying a signal associated with a selected aerial vehicle caninclude identifying a signal that directly (and/or closely) matches aknown audio signature 901, 902, 903 of the selected aerial vehicle.

However, as discussed herein the audio signature of the second aerialvehicle 305 (shown in FIGS. 5 and 6) can be perceived as being higher orlower depending on the Doppler effect. In other words, motion of thesignal source and/or detection system 100 relative to the first aerialvehicle 200 can change perceived frequency of sound received by thedetection system 100. Accordingly, in some embodiments, identifying thesignal associated with the aerial vehicle can include identifying asignal that matches a given audio signature but that has been shiftedeither higher or lower in frequency. For example, FIG. 13 illustratesgraphs 900D, 900E, 900F that show respective received signals 904, 905,906 that can be matched to the audio signatures 901, 902, 903 shown inFIG. 12.

Graph 900D shows a received signal 904 (dashed line) that can beidentified as corresponding to audio signature 901. In this example, thefrequency of the received signal 904 is shifted upward in frequencycompared to baseline frequency 901 because the second aerial vehicle 305is approaching the system 100 (see, e.g., FIG. 5).

Graph 900E shows a received signal 905 (dashed lines) that can beidentified as corresponding to audio signature 902. In this example, thefrequency of the received signal 905 is shifted downward in frequencycompared to baseline frequency 902 because the second aerial vehicle 305is moving away from the system 100 (see, e.g., FIG. 6). In this example,correspondence between baseline frequency 902 and received signal 905can be identified based on the number of signature peaks, similarintensity signature and/or the same shift distance of each of thesignature peaks.

Graph 900F shows a received signal 906 (dashed lines) that can beidentified as corresponding to audio signature 903. In this example, thefrequency of the received signal 906 is shifted upward in frequencycompared to baseline frequency 903 because the second aerial vehicle 305is approaching the system 100 (see, e.g., FIG. 5). In this example,correspondence between baseline frequency 903 and received signal 906can be also identified based on the number of signature peaks, similarintensity signature and/or the same shift distance of each of thesignature peaks.

Although naturally occurring audio signatures of aerial vehicles can beidentified (e.g., the audio signature of a motor and/or rotors), in someembodiments, aerial vehicles can include a speaker that broadcasts anaudio signature and/or other unique identifying signal such as a serialnumber, or the like. Such an audio signature can be an audio signatureas discussed above, including a pattern. For example, in one embodimentan audio signature can cycle between signatures 901, 902 and 903, witheach having a duration of one second. In another example, the audiosignature 903 can be broadcast on-and-off for one or more selected timeperiods to generate a pattern (e.g., like Morse code). Such an audiosignature can be subsonic, sonic, and/or supersonic. In someembodiments, unique audio signatures can be provided for each givenaerial vehicle (e.g., like a MAC address) so that each aerial vehiclecan be identified based on its associated unique audio signature.

Returning to FIGS. 7 and 8, the methods 400, 500 continue to block 600,where the position and velocity of the second aerial vehicle 305 isidentified. In decision block 430, a determination is made whether thesecond aerial vehicle 305 (shown in FIGS. 5 and 6) is on a collisioncourse with the first aerial vehicle 200 (shown in FIGS. 5 and 6). Forexample, the velocity and position of the first aerial vehicle 200 canbe compared to the determined velocity and position of the second aerialvehicle 305 to determine if a collision is possible.

If a determination is made that a collision course is not present, thenthe methods 400, 500 continues to block 440 where the current course ismaintained. However, if a determination is made that a collision courseis present, then the method 400 continues to block 450 where anavoidance maneuver is performed. Avoidance maneuvers can include anysuitable course correction or movement that can prevent a collision,including moving in the opposite direction from an approaching secondaerial vehicle 305; moving in an orthogonal direction from anapproaching second aerial vehicle 305; moving around an approachingsecond aerial vehicle 305; or hovering in place to allow the approachingsecond aerial vehicle 305 to pass.

At decision block 460, a determination is made whether the second aerialvehicle 305 has ended its flight, and if so, the methods 400, 500 aredone in block 499. However, if the flight of the second aerial vehicle305 is not ended, then the method 400 cycles back to block 420 (shown inFIG. 7), or alternatively, the method 500 cycles back to block 410(shown in FIG. 8) as discussed in more detail below. Accordingly, themethods 400, 500 continue while the first aerial vehicle 200 is flyingso that the first aerial vehicle 200 can continuously detect and avoidother aerial vehicles 305 that may be approaching or proximate.

In some embodiments, audio signals can be pro-processed to remove noise.For example, referring to FIG. 8, the method 500 begins, in block 410,where audio signals are processed to remove noise. In variousembodiments, microphones 112 of the array 110 can each receive arespective audio signal, and a noise audio signal received from thesecondary microphone 130 can be subtracted from the respective audiosignals received by the microphones 112 of the array 110.

In various embodiments, the noise signal received from the secondarymicrophone 130 is assumed to substantially represent background noiseand the audio signal from the microphones 112 of the array 110represents desirable target signal plus background noise. Accordingly,by subtracting the audio signal from the secondary microphone 130 fromthe respective audio signals from the microphones 112 of the array 110can leave desirable target signal.

Accordingly, it can be advantageous to position the array 110 on aselected portion of the UAV housing 201 (shown in FIG. 4) that isopposing and/or distal the portion of the UAV housing 201 upon which tothe secondary microphone 130 is positioned. The secondary microphone 130thereby primarily (and/or only) receives ambient background noiseinstead of background noise and target signal. For example, referring toFIGS. 5 and 6, a second aerial vehicle 305 is either approaching (asshown in FIG. 5) or moving away from (as shown in FIG. 6) the firstaerial vehicle 200. More specifically, the second aerial vehicle 305 iseither approaching or moving away from the array 110 positioned on thefirst side 315 of the housing 205 of the first aerial vehicle 200. Sound310 from the second aerial vehicle 305 therefore meets the array 110first and is substantially attenuated and/or blocked before reaching thesecondary microphone 130. In other words, the audio signals or sound 310from the second aerial vehicle 305 can be detected at a substantiallygreater level compared to the secondary microphone 130. The relativeplacement of the array 110 and the secondary microphone 130 can enablethe subtraction of the noise signal of the secondary microphone 130 fromthe audio signal of the microphones 112 of the array 110 results in thesound 310 emitted from the second aerial vehicle 305.

In contrast, in some embodiments, the noise signal of the secondarymicrophone 130 is not removed from audio signals obtained by the array110. The audio signals obtained by the array 110 thereby can beprocessed or otherwise handled as described herein without the noiseremoval, at 410. Stated somewhat differently, in some embodiments, thesystem 100 can omit the secondary microphone 130. For example, asdiscussed above, FIG. 7 is a flow diagram illustrating a method 400 ofaerial vehicle detection and avoidance in accordance with an alternativeembodiment, wherein noise may not be removed from received audiosignals.

FIG. 9 illustrates an exemplary embodiment 600A of the method 600 ofdetermining the position and velocity of a signal source such as thesecond aerial vehicle 305. In block 610, a directional analysis isperformed on a plurality of audio signals, and, in block. 620, anintensity analysis is performed on the audio signals. The directionalanalysis, at 610, can be performed in any suitable way, including themethods described in further detail below. The intensity analysis, at620, can include determining the relative intensity of audio signals.For example, received audio signals can be compared to a baselineintensity, which can be associated with a type of signal source.Intensity analysis can be configured to determine the relative distanceof a signal source, such as the second aerial vehicle 305, from thesystem 100.

In various embodiments, the position and velocity of a signal source canbe determined by observing changes of determined position of a signalsource including distance and/or direction of the signal source.

FIG. 10 illustrates an exemplary embodiment 600B of the method 600 ofdetermining the position and velocity of a signal source such as thesecond aerial vehicle 305. The method 600 begins, in block 710, where afrequency estimation of a first signal sample is conducted.

For example, assume that matrix A indicates the attributions of thesignal sources, (referred to as (A=(a₁,a₂, . . . ,a_(N)))), a_(i) is afunction of frequency (f) and/or incidence angle (θ). Further assumethat F represents source signals and W indicates noise. The compositesource and noise signal received can be indicated as X=AF+W. Assuming Rxindicates the covariance matrix of X, then the eigenvalues of Rx matrixare {λ₁, λ₂, . . . , λ_(N)}. If signal sources have D signals, thenamong the eigenvalues, N-D eigenvalues are equal. In other words,{λ_(D+1), λ_(D+2), . . . , λ_(D+N)} correspond to the noise space whileother D eigenvalues correspond to the signal space. Further assume thatE_(N) indicates eigenvectors corresponding to eigenvalues {λ_(D+1),λ_(D+2), . . . , λ_(N)} in Rx matrix. These eigenvectors indicate noisespace. The noise space and signal space can be necessarily orthogonal.Therefore, if the signal space and the noise space are orthogonal, theinner product of the signal space and the noise space will be 0.Additionally, assume that P(ω)=I/a*(ω)E_(N)E_(N)*a(ω) indicates thereciprocal of the inner product. The relationship between the change ofsignal power P with angular frequency ω is illustrated in FIG. 14, inwhich the frequency corresponding to each peak in the figure indicatesthe frequency of the respective sound sources.

In block 720, a signal direction of the first signal sample source canbe determined. For example, in one embodiment, the inner product of thesignal space and the noise space can be calculated. In contrast tofrequency estimation discussed above, the signal space here can alterwith the change of the incidence angle, which is represented byP(θ)=I/a*(θ)E_(N)E_(N)*a(θ). As shown in FIG. 15, the anglecorresponding to each peak indicates the direction of respective soundsources. The intensity of a signal is in proportion to this peak value.

In further embodiments, frequency estimation and signal directiondetermination can be performed in any suitable way. For example,frequency estimation and signal direction determination can occur aspart of implementation of a Multiple Signal Classification algorithm(MUSIC algorithm) (see, e.g., Schmidt, IEEE Transactions On Antennas AndPropagation, Vol. AP-34. No. 3, March 1986, which is incorporated hereinin its entirety for all purposes).

In block 730, frequency estimation of a second signal sample isconducted, and, in block 740, signal direction of the second signalsample source is determined. In block 750, a determination is madewhether the signal source is approaching or moving away from the firstaerial vehicle 200. For example, as illustrated in FIG. 5, where thesignal source (i.e., the second aerial vehicle 305) is moving toward thefirst aerial vehicle 200, also referred to as a sensing aerial vehicle200, the Doppler effect causes the frequency of sound 310A from thesecond aerial vehicle 305 to be perceived as being higher than when thesecond aerial vehicle 305 is stationary or moving away from the sensingaerial vehicle 200.

In contrast, as illustrated in FIG. 6, where the signal source (i.e.,the second aerial vehicle 305) is moving away from the sensing aerialvehicle 200, the Doppler effect causes the frequency of sound 310B fromthe second aerial vehicle 305 to be perceived as being lower than whenthe second aerial vehicle 305 is stationary or moving toward the sensingaerial vehicle 200.

In other words, signal source of the second aerial vehicle 305 movingtoward sensing aerial vehicle 200 causes sound waves 310A to becompressed and therefore perceived as having a higher frequency orhigher pitch. On the other hand, signal source of the second aerialvehicle 305 moving away from sensing aerial vehicle 200 causes soundwaves 310B to be expanded and therefore perceived as having a lowerfrequency or lower pitch. Accordingly, by comparing the frequency ofsequential signal source samples, whether the signal source isapproaching or moving away can be determined.

Additionally and/or alternatively, signal intensity can also be used todeterminate whether the signal source is approaching or moving away. Forexample, where signal intensity and the pitch of the signal increase, adetermination can be made that the signal source is approaching.Similarly, where signal intensity and the pitch of the signal decrease,a determination can be made that the signal source is moving away.

Therefore, according to the Doppler Effect, it can be determined whetherthe signal source is approaching or moving away. The intensity of asignal source can assist in such a determination. For example, if thefrequency is increasing and the intensity is going up, the signal sourcecan be determined to be approaching. Otherwise, the signal source can bedetermined to be moving away.

In block 760, the distance of the signal source from the primarymicrophone array 110 is determined. For example, in some embodiments,such a determination can be made based on the intensity of the signal.In other words, a louder signal can be determined to be closer than aquieter signal. In some embodiments, distance can calculated based on aknown or assumed distance and intensity values corresponding to a givensignal source. For example, if a determination is made that the signalsource is a UAV of “Type A,” the operating intensity of this UAV atvarious distances can be known and the intensity of a received signalcan be compared to these known values to estimate a distance value. Inother embodiments, distance values can be estimated based on assumedoperating intensities of a given signal source. In some embodiments,distances can be in units of distance (e.g., meters) or can be generallydescriptive of distance ranges (e.g., very far, far, close, very close,and the like).

In block 770, the current position and velocity of the signal source isdetermined. For example, such a determination can be based on one ormore signal direction determination, distance determination, and/orapproaching/moving away determination as discussed herein.

In block 780, the bearing of the signal source optionally can bedetermined. For example, in addition to calculating the current positionof a signal source as described above in reference to block 770, it canalso be advantageous to estimate the bearing or future position(s)and/or velocity/velocities of a signal source. Such a determination canbe based on one or more velocity determination, position determination,signal direction determination, distance determination, and/orapproaching/moving away determination as discussed herein.

In various embodiments, the determining the bearing of the signalsource, at 780, is absent. For example, FIG. 11 illustrates an exemplaryembodiment 600C of the method 600 of determining the position andvelocity of a signal source such as the second aerial vehicle 305,wherein the determining the bearing of the signal source is absent.

Additionally, any of the methods described herein can be embodied in acomputer product that is encoded on non-transitory machine-readablestorage media. For example, a non-transitory machine-readable storagemedia can comprise a portable memory device such as a flash drive, or amemory associated with a device such as the memory 122 that is part ofthe sensing device 120 shown in FIGS. 1 and 2. Such a computer productcan be executed by any suitable processing device, which can include theprocessor 121 that is part of the sensing device 120 shown in FIGS. 1and 2.

Additionally, although various embodiments discussed herein relate to afirst aerial vehicle 200 detecting a second aerial vehicle 305 (shown inFIGS. 5 and 6), in some embodiments, ground-vehicles, stations, ordevices can also comprise a detection system 100. In furtherembodiments, ground-vehicles, stations, or devices can be operablyconnected to one or more first aerial vehicle 200, which can beadvantageous for sharing data with the first aerial vehicle 200,including the position of other aerial vehicles 305 that may not beconfigured to share data.

For example, FIG. 16 is an exemplary network diagram that illustrates asystem 1100 including a first aerial vehicle 200 that is operablyconnected to a base station 1105 via a network 1110. The base station1105 and the first aerial vehicle 200 can each comprise a respectivedetection system 100. Accordingly, in various embodiments, one or bothof the base station 1105 and first aerial vehicle 200 can detect theposition and velocity of various objects, including the second aerialvehicle 305. Detecting of the position and velocity of the second aerialvehicle 305 by both the base station 1105 and first aerial vehicle 200can be advantageous because such detections can be shared via thenetwork 1110 and used to improve accuracy of a determined position andvelocity of the second aerial vehicle 305. Additionally, it may beadvantageous for the base station 1105 to detect the position andvelocity of the first aerial vehicle 200 so that such a position andvelocity can be provided to the first aerial vehicle 200 via the network1110 so that the first aerial vehicle 200 has data on its own positionand velocity.

FIGS. 17-20 depict examples of four alternative embodiments 1210, 1220,1230, 1240 of an aerial vehicle that includes selected combinations ofprimary microphone arrays 110 and secondary microphones 130. FIG. 17 isan exemplary alternative embodiment of a detection system 100 positionedon a first aerial vehicle 1210, where the detection system 100 includesa first and second primary microphone arrays 110 and a first and secondsecondary microphones 130 positioned on opposing sides of the aerialvehicle 1210 and pointing in opposite directions. Such an embodiment maybe advantageous for enhanced detection of signal sources approachingfrom opposing sides of the aerial vehicle 1210.

FIG. 18 is another exemplary alternative embodiment of a detectionsystem 100 positioned on a first aerial vehicle 1220, where thedetection system 100 includes a first and second primary microphonearrays 110 and a first and second secondary microphones 130 positionedperpendicularly on the aerial vehicle 1220 and pointing outwardly. Suchan embodiment may be advantageous for enhanced detection of signalsources approaching from different sides of the aerial vehicle 1220.

Accordingly, as illustrated in FIGS. 17 and 18, in some embodiments thedetection system 100 can include a first primary microphone arraypointed in a first direction; a first secondary microphone pointed in asecond direction; a second primary microphone array pointed in a thirddirection; and a second secondary microphone pointed in a fourthdirection. In various embodiments, at least two of the first, second,third and fourth directions can be different directions.

FIG. 19 is a further exemplary alternative embodiment of a detectionsystem 100 positioned on an aerial vehicle 1230, where the detectionsystem 100 includes a single primary microphone array 110. Such anembodiment may be advantageous where noise reduction via a secondarymicrophone 130 is not necessary.

FIG. 20 is a still further exemplary alternative embodiment of adetection system 100 positioned on a first aerial vehicle 1240, wherethe detection system 100 includes four separate primary microphonearrays 110 positioned on the aerial vehicle 1240. Such an embodiment maybe advantageous for enhanced detection of signal sources approachingfrom various sides of the aerial vehicle 1240, where noise reduction viaa secondary microphone 130 is not necessary.

The described embodiments are susceptible to various modifications andalternative forms, and specific examples thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the described embodiments are not to belimited to the particular forms or methods disclosed, but to thecontrary, the present disclosure is to cover all modifications,equivalents, and alternatives.

What is claimed is:
 1. A method of determining a position and a velocityof a signal source, comprising: obtaining a plurality of audio signalsfrom a primary microphone array arranged at a first location of a movingplatform; obtaining a noise audio signal from a secondary microphonearranged at a second location of the moving platform, the first locationand the second location being at opposing sides of the moving platform;generating a plurality of processed audio signals by subtracting thenoise audio signal from each of the plurality of audio signals;identifying, from the plurality of processed audio signals, a set ofprocessed audio signals that match an audio signature of the signalsource according to characteristics associated with the audio signature,the characteristics associated with the audio signature including anumber of signature peaks in the audio signature, intensities of thesignature peaks in the audio signature, and shift distances of detectedpeaks in the set of processed audio signals respectively fromcorresponding ones of the signature peaks in the audio signature;performing a direction analysis on the set of processed audio signals;performing a frequency analysis on the set of processed audio signals;estimating the position and the velocity of the signal source accordingto a result of the direction analysis and a result of the frequencyanalysis; and determining whether the signal source is on a collisioncourse with the moving platform according to the position and thevelocity of the signal source.
 2. The method of claim 1, furthercomprising: conducting a frequency estimation on the set of processedaudio signals; and determining a signal direction of the signal sourcebased on the set of processed audio signals.
 3. The method of claim 2,wherein the set of processed audio signals are a first set of processedaudio signals, the method further comprising: identifying, from theplurality of processed audio signals, a second set of processed audiosignals that match the audio signature of the signal source according tothe characteristics associated with the audio signature; and conductinga frequency estimation on the second set of processed audio signals. 4.The method of claim 3, wherein the signal direction is a first signaldirection, the method further comprising: determining a second signaldirection of the signal source based on the second set of processedaudio signals.
 5. The method of claim 4, further comprising: determiningwhether the signal source is approaching or moving away from a detectionposition by performing a Doppler analysis of the first and second setsof processed audio signals.
 6. A method of determining a position and avelocity of a signal source, comprising: obtaining a plurality of audiosignals from a primary microphone array arranged at a first location ofa moving platform; obtaining a noise audio signal from a secondarymicrophone arranged at a second location of the moving platform, thefirst location and the second location being at opposing sides of themoving platform; generating a plurality of processed audio signals bysubtracting the noise audio signal from each of the plurality of audiosignals; identifying, from the plurality of processed audio signals, afirst set of processed audio signals and a second set of processed audiosignals that match an audio signature of the signal source according tocharacteristics associated with the audio signature, the characteristicsassociated with the audio signature including a number of signaturepeaks in the audio signature, intensities of the signature peaks in theaudio signature, and shift distances of detected peaks in the set ofprocessed audio signals respectively from corresponding ones of thesignature peaks in the audio signature; conducting a frequencyestimation on the first set of audio signals; determining a first signaldirection of the signal source based on the first set of audio signals;conducting a frequency estimation on the second set of audio signals;determining a second signal direction of the signal source based on thesecond set of audio signals; determining whether the signal source isapproaching or moving away from a detection position by performing aDoppler analysis of the first and second sets of audio signals;determining the position and the velocity of the signal source based onthe Doppler analysis, a direction analysis, and an intensity analysis;and determining whether the signal source is on a collision course withthe moving platform according to the position and the velocity of thesignal source.
 7. An acoustic sensing system, comprising: a housing of amoving platform; a primary microphone array positioned at a firstlocation of the housing and comprising a plurality of microphones; asecondary microphone positioned at a second location of the housing andbeing operably connected to the primary microphone array, the firstlocation and the second location being at opposing sides of the housing;and a processing device configured to: obtain a plurality of audiosignals from the primary microphone array; obtain a noise audio signalsfrom the secondary microphone; generate a plurality of processed audiosignals by subtracting the noise audio signal from each of the pluralityof the audio signals; identify, from the plurality of processed audiosignals, a set of processed audio signals that match an audio signatureof the signal source according to characteristics associated with theaudio signature, the characteristics associated with the audio signatureincluding a number of signature peaks in the audio signature,intensities of the signature peaks in the audio signature, and shiftdistances of detected peaks in the set of processed audio signalsrespectively from corresponding ones of the signature peaks in the audiosignature; determine a position and a velocity of the signal sourcebased on a direction analysis and an intensity analysis of the set ofprocessed audio signals associated with the signal source, and determinewhether the signal source is on a collision course with the movingplatform according to the position and the velocity of the signalsource.
 8. The acoustic sensing system of claim 7, wherein the primarymicrophone array points in a first direction and the secondarymicrophone points in a second direction that is different from the firstdirection.
 9. The acoustic sensing system of claim 8, wherein the firstdirection is opposite to the second direction.
 10. The acoustic sensingsystem of claim 8, wherein the first direction is substantiallyperpendicular to the second direction.
 11. The acoustic sensing systemof claim 7, wherein microphones of the primary microphone array arepositioned on a substrate in a matrix configuration having rows andcolumns.
 12. The acoustic sensing system of any claim 7, wherein theprocessing device is further configured to: conduct a frequencyestimation on the set of processed audio signals; and determine a signaldirection of the signal source based on the set of processed audiosignals.
 13. The acoustic sensing system of claim 7, wherein theprocessing device is further configured to predict a future position anda future velocity of the based on a Doppler analysis, the directionanalysis and the intensity analysis of the set of processed audiosignals.
 14. The method of claim 1, wherein the audio signature includesa pattern of one or more frequency peaks.
 15. The method of claim 1,further comprising: comparing one or more intensities of the set ofprocessed audio signals with one or more baseline intensities associatedwith a type of the signal source to determine a relative distancebetween the signal source and the moving platform; and estimating theposition and the velocity of the signal source based on the relativedistance.
 16. The method of claim 1, further comprising: comparing oneor more intensities of the set of processed audio signals with one ormore baseline intensity associated with a type of the signal source atone or more known distance values to the signal source to determine arelative distance value between the signal source and the movingplatform; and estimating the position and the velocity of the signalsource based on the relative distance value.
 17. The method of claim 1,further comprising determining a type of the signal source.
 18. Themethod of claim 1, wherein types of microphones of the primarymicrophone array are different from a type of the secondary microphone.19. The method of claim 1, wherein: a frequency range of the pluralityof audio signals obtained by the primary microphone array include one ormore of subsonic frequency, sonic frequency, and ultrasonic; and afrequency range of the noise audio signal obtained by the secondarymicrophone includes one or more of subsonic frequency, sonic frequency,and ultrasonic.
 20. The method of claim 1, wherein the audio signatureuniquely identifies the signal source.